Papers by Author: Xin Wu

Abstract: The ultrasonic vibration assisted compression process is analyzed from the viewpoint of the impact dynamics. The typical metal forming patterns are studied based on the theory of wave propagation in solid. The effects of the geometry scale, friction, material parameters, ultrasonic amplitude and ultrasonic frequency on the forming process are analyzed. A combined parameter is proposed to evaluate the impact of the ultrasonic vibration on the specimen. The typical metal forming parttern are demonstrated by the experiment result of the literature.

Abstract: In metal forming process analysis, the accuracy loss is inevitable for complex boundary shape, un-uniformly distributed points and high velocity gradient distribution in analysis domain. In order to improve simulation accuracy, an h-adaptive procedure for the background required rigid (visco) plastic meshless Galerkin method is developed. A mixed posteriori error indicator is presented, which consists of a cell energy rate integration error estimator and a cell energy rate approximation error estimator to indicate the integration error and the approximation error, respectively. The corresponding local refinement strategies are developed, and the adaptive refining procedure is given. The adaptive procedure is applied only once in each time step simulation for the consideration of computational efficiency. A bulk forming process with severe metal deformation is analyzed. In comparison with the results obtained by using software Deform-2D, the effectiveness of the method developed in this paper is demonstrated.

Abstract: Combining element free Galerkin method with rigid/visco-plastic flow theory, the paper establishes the three-dimensional rigid/visco-plastic element free Galerkin method, and introduces it to analyze three-dimensional bulk metal forming processes. The velocity field is approximated by MLS method. Employing the incomplete generalized variation principle, stiffness matrix equation and solution formulas are derived. And STL format discrete triangular patches are used to describe the mould cavity. An analysis program for simulating three-dimensional bulk metal forming processes is developed. The program is capable of simulating three-dimensional unsteady bulk metal forming processes with severe deformation and arbitrarily shaped dies. A numerical example is analyzed. Numerical results such as material flow patterns and distributions of the effective stress are obtained. The effectiveness and validity of the proposed method and techniques are demonstrated by comparing with results obtained by using commercial finite element software.

Abstract: The meshless methods effectively deal with large material distortion simulation. Based on the rigid (visco)plastic material model, the element-free Galerkin method (EFGM) is introduced to simulate the metal forming processes. Aiming at the volume locking and pressure oscillation during EFGM analysis, a volumetric strain rate mapping method is proposed based on pressure projection method. The releasing algorithm is established by modifying the volumetric strain rate in the functional equation. The volumetric strain rate calculated according to velocity field is mapped onto a lower-order space to reduce the number of independent discrete constrain equations. The numerical example shows that the releasing algorithm can effectively eliminate the volumetric locking and pressure oscillation without the expense of employing large support size in the rigid-plastic meshless method.

Abstract: High quality Nd:YVO4 thin films were fabricated successfully by using a pulsed laser deposition technique. The properties of the samples were characterized by using X-ray diffraction, atomic force microscopy, and prism-coupling measurements. According to above discussion, we concluded the optimal preparation conditions for Nd:YVO4 films prepared on Si/SiO2 substrates.